Are humans psychologically prone to violence? Is there a part of the
human brain that makes us violent creatures by nature? What is the
difference between culture?s partake in violence in our lives, and
what we would feel by nature regardless?

Yes humans are prone to violence, it's a result of being forced to
exist within large groups.

Social pressures such as your false class consiousness make you
violent, mainly towards yourself however these feelings are
exteriorised when no more can be taken, similar to a dog that is hurt,
you feel compleled to strike at anyone who gets close to your pain.

It realy depends on what you define as violence, punching your brother
or sister in the head, for example, whilst beeing perceived as violent
is undoubtably funny in the right circumstances.

Anyway not all violence is bad. Relatively speaking there is no peace
without war, because you have no comparison. In the same way violence
is mearly the oposite of ... non-violence.

Humans and indeed all higher order animals are prone to violence,
however it is nothing to do with our social existence.  In fact social
animals tend to develop control schemes to stop violence escalating to
the detriment of the species, so in many ways social animals tend to
develop "stylised" displays as a way to avoid unnecessary conflict.

The true root of violence appears to be the so-called "fight or
flight" response - a combination of the sympathetic/para-sympathetic
nervous system and the hypothalamus/adrenal axis.

The sympathetic nervous system is the system that elevates heart rate
and other similar physiological effects when you are given a fright. 
Your body is in essence prepared to maximise its performance in a
combat, injury, extreme exercise situation.  The para-sympathetic
nervous system is what of course the converse, used to calm your body
back down when the situation is assessed as no longer threatening,
hence minimising damage to the body and conserving energy for a later
crisis.

The Hypothalamus is often associated with PTSD (Post Traumatic Stress
Disorder) whereby the hypothalamus (responsible for translating
extreme emotions into suitable physical responses) becomes
over-sensitised.  This results in extreme over-reaction to small
non-threatening stimuli - be it the ex-soldier who cowers at the sound
of a helicopter or the abused child who has reacts to affection with
aggression.  This affect has been linked by some researchers to the
degree of dissasociation the victim inccurs during the crisis, those
who are most aware and conscious of the incident are the least likely
to have future issues with PTSD.

A few introductory resources can be found here, but there are very
good in depth discussions of many of these issues freely available:

http://allpsych.com/psychology101/brain.html
http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgeneral%2Fans_003.html
http://www.answers.com/topic/fight-or-flight-response
http://www.answers.com/main/ntquery;jsessionid=161ia6dwnna8m?method=4&dsid=2222&dekey=Hypothalamic-pituitary-adrenal+axis&curtab=2222_1&sbid=lc05b

You can also look at it from the perspective of MBTI personality types:
http://www.personalitypage.com/info.html

There is always conflict between people who are more ordered(J) types,
and people who are perceiving/chaotic(P).  The Intuitive(N) vs
Sensing(S) types also conflict strongly.

But, it takes all types to make the world go around.  You just have to
hope that they can learn to respect each other.

Cheers,
LP